Inkjet printing mechanisms often use moveable cartridges, also called pens, that use one or more printheads formed with very small nozzles through which drops of liquid ink (e.g., dissolved colorants or pigments dispersed in a solvent) are fired. To print an image, the carriage traverses over the surface of the print medium, and the ink ejection elements associated with the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The pattern of pixels on the print media resulting from the firing of ink drops results in the printed image.
In multiple pass print modes, printhead nozzles can pass over the same media position several times. When a nozzle is defective, that is, for some reasons fails to operate properly, a multiple pass print mode allows the opportunity for other nozzles to cover for the defective nozzle and print on the media without noticeable degradation of quality.
When using single pass modes or when printheads are fixed it can be more difficult to compensate for a nozzle that fails to operate properly. Failure to compensate for a defective nozzle can lead to degraded print output that can show banding or other undesired printing effects.